Real-time correction of betatron tune ripples on a slowly extracted beam

In the main ring (MR) of the Japan Proton Accelerator Research Complex (J-PARC), the power supplies of magnets induce large ripples in the betatron tunes. The tune ripples degrade the quality of the beam spill on the slowly extracted beam. To improve the spill quality, the J-PARC MR employed a feedback system using a beam spill monitor; however, the existing system could not correct the beam spills suitably, since the tune ripples were too large. We developed a new correction system using the information of magnet currents as an input of the correction. The new system consists of current monitors and a corrector quadrupole, and it allows us to correct the ripples in real time. Using this system, we successfully corrected the tune ripples for the first time in the J-PARC MR. The correction system improved the spill quality from 3% (without any correction) to 30% (with the new correction), whereas the quality using the present feedback system is 17.4%.